local-id is not defined in the symbol syntax

[ZiyaoWei]

scip.md defines the syntax for symbols as

<symbol>               ::= <scheme> ' ' <package> ' ' (<descriptor>)+ | 'local ' <local-id>

However, <local-id> is not defined in the same section. Can we add it? I imagine it would be \d+ but would be good to have it in the official spec.

Note: the current actually makes the syntax ambiguous since <local-id> could potentially contain anything, and <scheme> could be local - I don't anybody sane would do that but technically it is a source of confusion.